1. Field of the Invention
The invention relates to wastewater treatment systems and methods of their operation and, more particularly, to systems and methods of control of wastewater treatment.
2. Description of the Related Art
Typically, wastewater streams, from municipal and industrial sources, contain waste matter such as solids and soluble and insoluble organic and inorganic materials. These wastewater streams require decontamination to meet regulatory requirements before they enter the environment. Decontamination in wastewater treatment systems typically involves pretreatment, primary treatment and secondary treatment. Pretreatment may involve equalization, neutralization and insoluble organic removal. Primary treatment may involve screening or sedimentation systems and other methods to remove fine, medium and large sized particles.
In some wastewater treatment systems, secondary treatment involves biological digestion or biological treatment. Specifically, biological wastewater treatment systems typically employ biomass with bacteria to digest biodegradable material in conventional sequencing batch flow, treatment systems. These systems, frequently, aerate wastewater in the presence of the bacteria and subsequently clarify the liquid before discharge to the environment.
For example, Goronszy, in U.S. Pat. No. 5,989,428, discloses a method and apparatus for treating waste material using a reactor or a series of reactors. The influent is treated by controlling the metabolic activity of the microorganisms by monitoring the oxygen utilization rate or the potential oxygen utilization rate of the biomass so as to determine the required amount of oxygen to be supplied to the biomass.
In another patent, Goronszy, in U.S. Pat. No. 5,013,441, discloses a biological nutrient removal system with sludge-bulking control in a batch-activated sludge system. The activated sludge sewage treatment process is received into a sewage treating basin in a first zone into which activated sludge is mixed and retained for a period sufficient to form a non-bulking sludge and absorb biodegradable dissolved compounds. It is aerated and subjected to a quiescent condition to permit settling of the sludge in a zone that has less than approximately 20% of the biochemical oxygen demand of the original sewage.
In most cases, these systems treat a normal flow of incoming wastewater. However, variations in flow conditions and contaminant concentration in the incoming wastewater streams, typically known as the influent or influent stream, periodically occur. Under normal conditions, wastewater flow varies because of ordinary fluctuations in household water use and discharge. However, rainstorms draining into a wastewater collection system, in many instances, produce higher than normal wastewater flow. Although these high flow situations occur infrequently, about 10 to 25% of the time on a yearly basis, wastewater treatment facilities must be flexible and accommodate such overflows.
Efforts to develop wastewater treatment systems that respond to high flow rates have been disclosed. For example, Loy et al., in U.S. Pat. No. 5,639,371, disclose an aeration reactor having two or more cells connected in series with a clarifier. When the flow rate of the incoming wastewater exceeds a selected level, incoming wastewater flows into the second cell until the surge has subsided.
Also, Timpany, in U.S. Pat. No. 5,902,484, describes a system for biologically treating wastewater by a modified activated sludge process in at least two treatment cells hydraulically connected in series. The first cell is a feed cell for incoming untreated wastewater and the last cell is the discharge cell for settling of suspended solids. The last cell has a means to transfer mixed liquor suspended solids and partially treated wastewater back to a prior treatment cell. Timpany discloses a method involving feeding wastewater through a plurality of treatment cells hydraulically connected in series, aerating in at least one cell, settling of suspended solids from at least one treatment discharge cell, and transferring mixed liquor suspended solids back to at least one previous cell.
Calltharp, in U.S. Pat. No. 5,021,161, discloses a process strategy for the treatment of a sequencing batch reactor wherein wastewater, in quantities above a pre-selected minimum amount, is proportionally aerated. Topnik, in U.S. Pat. No. 5,205,936, discloses sequencing batch reactors with volumetrically controlled withdrawals. A storm control procedure shortens the cycle times according to the magnitude of the rate. These systems differ from conventional sequencing batch flow, treatment systems and consequently require substantial capital costs compared to conventional sequencing batch flow, treatment systems.
In accordance with one embodiment, the invention relates to a wastewater treatment system having a flow control comprising an influent system with an influent flow. The wastewater treatment system also includes a wastewater treatment apparatus fluidly connected to the influent system and has a pump and a valve. The wastewater treatment system also comprises a regulating apparatus controlling one of the pump and the valve and comprises a controller and an input apparatus for providing an input signal which represents an influent flow. The controller analyzes the input signal and generates an output signal configured for one of a batch flow mode and a continuous flow mode.
The invention also provides a control system for regulating a wastewater treatment system. The control system comprises an input apparatus connected to the wastewater treatment system for transmitting an input signal corresponding to an influent flow. The control system further comprises a microprocessor for receiving and analyzing the input signal according to a logic program code and generating an output signal corresponding to one of a batch flow mode and a continuous flow mode. The control system also has an output apparatus for receiving the output signal and actuating a valve to regulate a flow in the wastewater system in one of the batch and the continuous flow modes.
In another embodiment, the invention provides a method for treating a wastewater stream comprising introducing the wastewater stream into a wastewater treatment system and measuring a rate of wastewater stream flow. The method also comprises controlling the wastewater treatment system in one of a batch flow mode and a continuous flow mode according to the measured rate.
In yet another embodiment, the invention provides a method for controlling a wastewater treatment system comprising introducing a wastewater stream into the wastewater treatment system and transmitting a process signal corresponding to an operating condition in the wastewater treatment system. The method further comprises analyzing the process signal and providing an output signal corresponding to one of a batch flow mode of operation and a continuous flow mode of operation according to a set of predetermined conditions. The method also actuates a valve based on the output signal.
Also disclosed is a method for controlling a wastewater treatment system comprising transmitting a process signal from the wastewater treatment system corresponding to one of a first influent flow rate and a second influent flow rate. The method also comprises sequencing the periods of treatment of the wastewater treatment system in a batch flow mode during the first influent flow rate and sequencing the periods of treatment of the wastewater treatment system in a continuous flow mode during the second influent flow rate. In this embodiment, the second influent flow rate is greater than the first influent flow rate.